1. Field of the Invention
The invention relates to an internal combustion engine in which the oil that collects in an oil pan is supplied to lubrication sites through operation of an oil pump.
2. Description of the Related Art
Usually, an oil pan is mounted on a lower portion of an internal combustion engine in a vertical direction, and an oil for lubrication collects in the oil pan. Then, the oil is pressure-fed from the oil pan through operation of an oil pump so as to be supplied to lubrication sites of the internal combustion engine, such as the bearing portions of the crankshaft, and the like. Besides, a construction is provided in which the oil having used for lubrication of lubrication sites runs down from the lubrication sites to collect in the oil pan.
In such an internal combustion engine, gas (e.g., air, the blow-by gas, etc.) in its interiors (e.g., the interior of the crankcase) inevitably mixes into the oil. If such a gas having mixed into the oil forms bubbles in the oil, the bubbles become a factor that brings about a decline of the pressure-feeding or pumping performance of the oil pump and therefore a decline of the lubrication performance, etc.
Therefore, a device for removing bubbles from oil is proposed in Japanese Patent Application Publication No. 2005-171921 (JP-A-2005-171921). This device is equipped with a depressurization chamber which is defined within the oil pan and into which oil flows. Oil is sucked into the oil pump via the depressurization chamber. Besides, an oil inlet opening that is formed in the depressurization chamber functions as a so-called throttle. Then, in the foregoing device, the decline of pressure associated with the inflow of oil into the depressurization chamber promotes the separation of bubbles from the oil. Therefore, the oil from which bubbles have been separated is sucked into the oil pump.
In the foregoing device, during operation of the oil pump, that is, during operation of the internal combustion engine, the foregoing oil inlet opening functions as a throttle. Therefore, inconveniences, such as an increase of the operation load on the oil pump, and a thereby-caused increase of the fuel consumption of the internal combustion engine, etc., are likely to come about, in comparison with an internal combustion engine that is not equipped with the depressurization chamber. Thus, this device cannot be said to efficiently separate bubbles from oil. In this respect, there is a room for betterment.